The story of the various metaseries revolves around the reincarnated defenders of a kingdom that once spanned the solar system, and around the evil forces that they battle. The major characters—(called Sailor Scouts in many Western versions)—are teenage girls who can transform into heroines named for the moon and planets (Sailor Moon, Sailor Mercury, Sailor Mars, etc). The use of "Sailor" comes from a style of girls' school uniform popular in Japan, the Japanese school uniform (sailor outfit), after which the Scout's uniforms are modeled. The elements of fantasy in the series are heavily symbolic and often based on mythology.